Hiya Chris!
Just how easy is it to learn Castellano in Barcelona? I mean, isn't the majority language spoken there Catalán? If you are already living in Barcelona, why do you want to go to an immersion school? Why dontcha move to a city where you can actually live eat and breathe Castellano?
I'm not criticizing Barcelona. It's an awesome city! If you're goal is to learn castellano, why Barcelona?